Mutation of CarO participates in drug resistance in imipenem-resistant Acinetobacter baumannii

Objective Acinetobacter baumannii has become an important problem because of the high drug resistance rate. The aim of this study was to assess the antimicrobial resistance profile and explore the role of membrane porin in imipenem resistance of A baumannii. Methods A total of 63 isolates of imipenem-resistant A baumannii (IRAB) and 21 of imipenem-sensitive A baumannii (ISAB) were collected. Susceptibility testing to 16 kinds of antimicrobial agents was conducted by K-B method. PCR technique was used to detect carO and oprD genes, and sequencing was performed to compare the sequence between IRAB and ISAB. Three-dimensional structure model of CarO protein was established. Results While ISAB isolates presented sensitive to most classes of antibiotics, isolates of IRAB displayed much higher resistance rate except tigecycline (3.2%), cefoperazone/sulbactam (28.6%), and minocycline (30.2%). All 84 isolates were observed carrying both carO and oprD genes. Further sequencing revealed important mutations of carO gene existed in IRAB in comparison with ISAB. Meanwhile, significant differences in three-dimensional structure of carO protein molecule were also found between IRAB and ISAB. Conclusions The drug resistance profile of IRAB is increasingly severe in clinical settings. Mutation of CarO was identified as one of the molecular mechanisms involved in imipenem resistance in A baumannii.